PHYSICS - boszik.net · Logic, and (iii) Mathematical methods and accuracy. Selected Reference...

PHYSICS CAPE, UNIT II Page of 1 5

HAMPTON SCHOOLCAPE STUDIES

PHOTOELECTRIC EFFECTWORKSHEET #16 (MAR. 2020)

Tutor: G. David Boswell

Instructions: Please work neatly, draw appropriately labelled diagrams, show all working and explanations, and use correct units. In general, apply relevant (i) Use of Knowledge, (ii) Reasoning and Logic, and (iii) Mathematical methods and accuracy.

Selected Reference Constants

Question 1. A-Level Physics International

(a) Albert Einstein did his Nobel prize award work in the area of quantum physics. This questions

addresses some of his major contributions to the development of this special branch of physics.

(i) What is the Duality of Matter? [3]

(ii) State the mathematical equation that describes the photoelectric effect stating all

symbols used. [4]

(iii) What is the Photoelectric Effect? State any 2 of the 4 ways in which it supports the

particulate theory of matter. [3]

(iv) Draw and fully label an experimental setup employing a simple photocell that can be

used to demonstrate the photoelectric effect. [5]

(v)

e = −1.60 ×10−19 C kc = 9.00 ×109 N ⋅m2 ⋅C−2 ε0 = 8.85 ×10−12 Fm−1 or C 2N −1m−2

g = 9.80 N ⋅ kg−1 c = 3.00 ×108 ms−1 µ0 = 4π ×10−7 Hm−1 or N ⋅A−2

h = 6.63×10−34 J ⋅s 1 u = 1.66×1027 kg 1 u = 931 MeV

NA = 6.02×1023 mol−1 me = 9.11×10−31 kg

© G. David Boswell | BÖ§ZïK Inc.™ Given: Mar 06, 2020 Due: Mar 11, 2020 Hampton School

PHYSICS

3.6 Photoelectric Effect 103

1. Thermionic emission: Application of heat allows electrons to gain enough energy to escape.

2. Secondary emission: The electron gains enough energy by transfer from a high-speed particle that strikes the material from outside.

3. Field emission: A strong external electric field pulls the electron out of the material.

4. Photoelectric effect: Incident light (electromagnetic radiation) shining on the material transfers energy to the electrons, allowing them to escape.

It is not surprising that electromagnetic radiation interacts with electrons within metals and gives the electrons increased kinetic energy. Because elec-trons in metals are weakly bound, we expect that light can give electrons enough extra kinetic energy to allow them to escape. We call the ejected electrons photo-electrons. The minimum extra kinetic energy that allows electrons to escape the material is called the work function f. The work function is the minimum bind-ing energy of the electron to the material (see Table 3.3 for work function values for several elements).

Experimental Results of Photoelectric EffectExperiments carried out around 1900 showed that photoelectrons are produced when visible and/or ultraviolet light falls on clean metal surfaces. Photoelectricity was studied using an experimental apparatus shown schematically in Figure 3.11. Incident light falling on the emitter (also called the photocathode or cathode)

Methods of electron emission

Photoelectrons

Work function

Element ! (eV) Element ! (eV) Element ! (eV)

Ag 4.64 K 2.29 Pd 5.22 Al 4.20 Li 2.93 Pt 5.64 C 5.0 Na 2.36 W 4.63 Cs 1.95 Nd 3.2 Zr 4.05 Cu 4.48 Ni 5.22 Fe 4.67 Pb 4.25

From Handbook of Chemistry and Physics, 90th ed. Boca Raton, Fla.: CRC Press (2009– 10), pp. 12-114.

Tab le 3 .3 Work Functions

Incident!light

Ammeter

I

A

Collector

e!

Emitter

Vacuum tube

Power supply

(Voltage V )

Figure 3.11 Photoelectric ef-fect. Electrons emitted when light shines on a surface are collected, and the photocurrent I is mea-sured. A negative voltage, relative to that of the emitter, can be ap-plied to the collector. When this retarding voltage is sufficiently large, the emitted electrons are repelled, and the current to the collector drops to zero.

03721_ch03_084-126.indd 10303721_ch03_084-126.indd 103 9/29/11 9:30 AM9/29/11 9:30 AM


(b) “Metal X has a work function of .”

(i) What does this statement mean? [1]

(ii) Calculate the maximum kinetic energy of electrons ejected from a magnesium surface

by ultraviolet radiation of frequency . [5]

(iii) Explain whether or not electrons are not emitted when radiation of frequency

falls on a surface of Metal X. Justify your answer with a calculation. [4]

[25 marks]

Question 2. CAPE 2018 Paper 2 Question 6 Pp. 24 - 25

(a) Describe the phenomenon of photoelectric emission. [3]

(b) Define EACH of the following quantities associated with photoelectric emission and state

EACH unit of measurement.

(i) Work function [3]

(ii) Cut-off wavelength [2]

(c) Light of wavelength is incident on a polished metal surface.

(i) Derive an expression for the maximum speed of the photoelectrons ejected. [4]

(ii) Calculate the maximum speed of the ejected photoelectron when , if the

metal is tin and has a work function of 5.5 eV. [3]

[15 marks]

4.01×10−19 J

1.23×1015 Hz

8.21×1014 Hz

λ

λ =100 nm



Question 3. CAPE 2017 Paper 2 Question 3 Pp. 12 - 13

(a) Figure 4 shows an experiment to demonstrate photoelectric effect.

What do the labels P, Q and R shown?

P ……………………………………………. [1]

Q ……………………………………………. [1]

R ……………………………………………. [1]

(b) The graph on Figure 5 below was obtained from a plot of the stopping potential, (volts),

against frequency, (Hz), of incident radiation in the experiment in (a) using an unknown

metal.

(i) Determine the slope of the graph in units. [4]

(ii) With the aid of the graph in Figure 5, formulate the algebraic equation relating the

stooping potential, , for the frequency, , of the incident radiation. [3]

(iii) What does the slope of the graph represent? [1]

(iv) From the graph, determine the threshold wavelength for the unknown metal. [4]

VS

f

SI

VS f



[15 marks]

TOTAL 55 marks

- ENFIN -© G. David Boswell | BÖ§ZïK Inc.™ Given: Mar 06, 2020 Due: Mar 11, 2020 Hampton School


MODERN PHYSICS

“I thus arrived at the following overall concept which guided my studies: for both matter and

radiations, light in particular, it is necessary to introduce the corpuscle concept and the wave concept

at the same time.”

Louis de Broglie, 1929

- ENFIN -


PHYSICS - boszik.net · Logic, and (iii) Mathematical methods and accuracy. Selected Reference...

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